Devices for fixing toner images on a recording medium (fixing station) for electrographic printers or copiers, with which devices toner images are fixed on a recording medium, for example paper, are known. An example of such a device is described in DE 198 27 210 C1. In this document, various fixing methods are likewise described. For example, fixing can be achieved by way of heat-pressure-fixing, in which the toner images are heated on the recording medium by a heating device and are then firmly bonded under pressure to the recording medium by fixing drums. In order to accelerate the fixing operation, a preheating saddle with which the recording medium and the toner images are preheated can be arranged upstream of the heating device. Further, the fixing can be effected by heating modules, which emit heat radiation directed to the recording medium and the toner images. Examples of such heating modules are foil radiators or ceramic panel radiators. These can be used with or without a preheating saddle. A detailed description of these fixing methods can in particular be taken from the document DE 198 27 210 C1 or WO 01/98840, which are incorporated by reference into the present application.
With the speed increase in printers making use of heat-pressure fixing rising more and more, problems arise regarding the preheating of the recording medium, since altogether enough heat energy for fixing is transferred with increasingly decreasing interaction time in the gap between the fixing drums. As a result, the length of the preheating saddle (contact heat transfer) would have to be increased and its temperature would have to be raised, which—for constructural reasons—is not always possible to a sufficient extent. In addition, when using printers in Twin Systems and when printing on both sides, a problem arises in particular during standstill. Since at higher printing speeds, the cooling time between the successive printers in the Twin System decreases, the recording medium comes to a halt in the second printer with an increased temperature in the case of a print stop and takes up additional heat while lying on the heating saddle of the second printer. When printing on both sides, the printed recording medium will in some cases stick on the backing due to the direct contact between the toner and the preheating saddle. As a result, the recording medium tears upon reapplication, and toner adhering on the preheating saddle has to be cleaned off at great expense.
The above-mentioned problem can be avoided by an optimized temperature control in the heating device. However it is difficult to achieve such a temperature control in known heating devices due to additional dependencies such as paper moisture, indoor climate, paperweight etc.